You say 'Hello' to someone when you meet them.
Hello, Trish. I won't shake hands, because I'm filthy.
你好,特里斯。我就不握手了,我的手好脏。
You say 'Hello' to someone at the beginning of a telephone conversation, either when you answer the phone or before you give your name or say why you are phoning.
A moment later, Cohen picked up the phone. 'Hello?'
一会儿之后,科恩拿起电话。“喂?”
You can call 'Hello' to attract someone's attention.
Very softly, she called out: 'Hello? Who's there?'
她很轻柔地喊道:“喂?谁在那儿?”
hellos
A hello is a greeting you use when meeting someone.
The salesperson greeted me with a warm hello.
那位推销员向我热情地打了个招呼。